Switched-capacitor circuit control in power converters

ABSTRACT

An apparatus for power conversion comprises a voltage transformation element, a regulating element, and a controller; wherein, a period of the voltage transformation element is equal to a product of a coefficient and a period of the regulating circuit, and wherein the coefficient is selected from a group consisting of a positive integer and a reciprocal of said integer.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/309,003, filed on Jun. 19, 2014 and issued as U.S. Pat. No. 9,143,037on Sep. 22, 2015, which is a continuation of PCT/US2012/070555, filed onDec. 19, 2012 which claims the benefit of the priority date of U.S.Provisional Application No. 61/577,271 filed on Dec. 19, 2011, thecontents of which are herein incorporated by reference.

FIELD OF DISCLOSURE

This disclosure relates to the control of power converters that utilizecapacitors to transfer energy.

BACKGROUND

Power converters may generally include switches and one or morecapacitors. Such converters can be used, for example, to power portableelectronic devices and consumer electronics.

A switch-mode power converter is a specific type of power converter thatregulates an output voltage or current by switching energy storageelements (i.e. inductors and capacitors) into different electricalconfigurations using a switch network.

A switched capacitor converter is a type of switch-mode power converterthat primarily utilizes capacitors to transfer energy. In suchconverters, the number of capacitors and switches increases as thetransformation ratio increases.

Typical power converters perform voltage transformation and outputregulation. In many power converters, such as buck converters, bothfunctions take place in a single stage. However, it is also possible tosplit these two functions into two specialized stages. Such two-stagepower converter architectures feature a separate transformation stageand a separate regulation stage. The transformation stage transforms onevoltage into another voltage, while the regulation stage ensures thatthe output voltage and/or output current of the power convertermaintains desired characteristics.

For example, referring to FIG. 1, in one known power converter 10, aswitched capacitor element 12A is electrically connected, at an inputend thereof, to a voltage source 14. An input of a regulating circuit16A is electrically connected to an output of the switched capacitorelement 12A. A load 18A is then electrically connected to an output ofthe regulating circuit 16A. Such a converter is described in US PatentPublication 2009/0278520, filed on May 8, 2009, the contents of whichare herein incorporated by reference.

Furthermore, a modular multi-stage power converter architecture isdescribed in PCT Application PCT/2012/36455, filed on May 4, 2012, thecontents of which are also incorporated herein by reference. Theswitched capacitor element 12A and the regulating circuit 16A can bemixed and matched in a variety of different ways. This provides atransformative integrated power solution (TIPS™) for the assembly ofsuch power converters. As such, the configuration shown in FIG. 1represents only one of multiple ways to configure one or more switchedcapacitor elements 12A with one or more regulating circuits 16A.

FIG. 2 illustrates a power converter 10A that receives an input voltageVIN from the voltage source 14 and produces an output voltage VO that islower than the input voltage VIN. The power converter 10A is aparticular embodiment of the power converter architecture illustrated inFIG. 1. The switched capacitor element 12A features a 2:1 dual-phaseseries-parallel switched capacitor network that includes power switchesS1-S8 and pump capacitors C1-C2. In contrast, the regulating circuit 16Afeatures a buck converter that includes a low-side switch SL, ahigh-side switch SH, a filter inductor L1, and a driver stage 51.

In the operation of the switched capacitor element 12A, the powerswitches S1, S3, S6, S8 and the power switches S2, S4, S5, S7 are alwaysin complementary states. Thus, in a first network state, the powerswitches S1, S3, S6, S8 are open and the power switches S2, S4, S5, S7are closed. In a second network state, the power switches S1, S3, S6, S8are closed and the power switches S2, S4, S5, S7 are open. The switchedcapacitor element 12A cycles through the first network state and thesecond network state, resulting in an intermediate voltage VX that isone-half of the input voltage VIN.

Referring to FIG. 2, the switched capacitor element 12A is in the firstnetwork state when a first phase voltage VA is low and a second phasevoltage VB is high. In contrast, the switched capacitor element 12A isin the second network state when the first phase voltage VA is high andthe second phase voltage VB is low. The two phase voltages VA, VB arenon-overlapping and have approximately a fifty percent duty cycle.

In the operation of the regulating circuit 16A, the low-side switch SLand the high-side switch SH chop the intermediate voltage VX into aswitching voltage VLX. A LC filter receives the switching voltage VLXand generates the output voltage VO that is equal to the average of theswitching voltage VLX. To ensure the desired output voltage VO, aregulation control voltage VR controls the duty cycle of the low-sideswitch SL and the high-side switch SH. Additionally, the driver stage 51provides the energy to open and close the low-side and high-sideswitches SL, SH.

Previous disclosures treat the control of the switched capacitor element12A and regulating circuit 16A separately. This has numerousdisadvantages, one of which is that the intermediate voltage VX ripplewill feed through to the output voltage VO. A possible solution to thisproblem is to create a feed-back control loop that is fast enough toattenuate the effect of the intermediate voltage VX ripple on the outputvoltage VO. To achieve this goal, the frequency of the regulatingcircuit 16A must be at a significantly higher frequency than thefrequency of the switched capacitor element 12A.

Another possible solution to this problem would be to add a feed-forwardcontrol loop to the regulating circuit 16A. However, as was the casewith the fast feed-back solution, the feed-forward solution will only beeffective if the frequency of the regulating circuit 16A issignificantly higher than the frequency of the switched capacitorelement 12A. Therefore, both solutions place a severe frequencyconstraint on the switched capacitor element 12A and the regulatingcircuit 16A.

Furthermore, there is typically a dead-time interval DT between thefirst network state and the second network state of the switchedcapacitor element 12A. During the dead-time interval DT, all of theswitches in the switched capacitor element 12A are open. This ensures aclean transition between the first network state and the second networkstate of the switched capacitor element 12A, and vice versa. If theregulating circuit 16A tries to draw current during the dead-timeinterval DT, a voltage ‘glitch’ will occur at the node between theswitched capacitor element 12A and the regulating circuit 16A.

The voltage ‘glitch’ can be reduced through the use of a glitchcapacitor CX. Unfortunately, a portion of the energy stored on theglitch capacitor CX is thrown away each time the switched capacitorelement 12A transitions between the first network state and the secondnetwork state, and vice versa. The energy loss is a result of the glitchcapacitor CX being shorted to capacitors at a different voltage, such aspump capacitors C1, C2. Therefore, the use of a glitch capacitor CX tosupply energy during the dead-time interval DT is an effective solution,but requires one additional capacitor and reduces the efficiency of thepower converter 10A.

SUMMARY

In one aspect, the invention features an apparatus for power conversion.Such an apparatus includes a first element configured to accept an inputsignal having a first voltage and to output an intermediate signalhaving a second voltage, and a second element configured to receive theintermediate signal from the first element and to output an outputsignal having a third voltage. The first element is either a voltagetransformation or a regulating element. The second element is aregulating element when the first element is a voltage transformationelement and a voltage transformation element otherwise. A controller isconfigured to control a period of the voltage transformation element anda period of the regulating element. The controller is configured tosynchronize the period of the voltage transformation element with aproduct of a coefficient and the period of the regulating element. Thiscoefficient can be either a positive integer or a reciprocal of theinteger.

In some embodiments, the coefficient is a positive integer, whereas inothers, it is a reciprocal of the positive integer.

Embodiments also include those in which the controller receives theintermediate signal from the first element and the output signal fromthe second element. Among these are those in which the controllerreceives the input signal, and also those in which the controllergenerates a first control signal based on the output signal and sendsthe first control signal to the regulating element. This embodiment alsoincludes within its scope alternative embodiments in which thecontroller generates a second control signal based on the intermediatesignal and the first control signal, and sends the second control signalto the voltage transformation element.

Also included within the scope of the invention are those embodiments inwhich the controller provides linear voltage-mode control, and those inwhich it provides peak current-mode control.

In some embodiments, regulating element passes continuous currenttherethrough, whereas in others, the regulating element passesdiscontinuous current therethrough.

In other embodiments, the voltage transformation element includesvoltage transformation sub-elements and the regulating element includesregulating sub-elements, and each voltage transformation sub-element isassociated with a corresponding one of the regulating sub-elements.

Embodiments also include those in which the first element includes avoltage transformation element and those in which the first elementincludes a regulating element.

In another aspect, the invention features an apparatus for powerconversion, such an apparatus includes a voltage transformation element,a regulating element, and a controller. A period of the voltagetransformation element is equal to a product of a coefficient and aperiod of the regulating circuit. The coefficient is either a positiveinteger or a reciprocal of the integer.

Embodiments include those in which the regulating element passescontinuous current therethrough, and also those in which the regulatingelement passes discontinuous current therethrough.

In some embodiments, the controller controls multiple phases present inthe regulating element and the voltage transformation element.

Other embodiments include a data processing unit and a memory unit, atleast one of which is configured to consume power provided by the powerconverter circuit.

Additional embodiments include data processing unit, a display, and awireless transmitter and receiver, at least one of which is configuredto consume power provided by the power converter circuit.

DESCRIPTION OF THE FIGURES

The foregoing features of the circuits and techniques described herein,may be more fully understood from the following description of thefigures in which:

FIG. 1 shows a known power converter architecture;

FIG. 2 shows a particular implementation of the power converterarchitecture in FIG. 1;

FIG. 3 shows a controller coupled to the power converter in FIG. 2;

FIG. 4 shows a particular implementation of the controller in FIG. 3;

FIG. 5 shows a timing diagram of relevant signals from the embodiment inFIG. 4.

FIG. 6 shows a close-up of selected signals in FIG. 5;

FIG. 7 shows a DC model of a switched capacitor element;

FIGS. 8A-8B show the relationship between the load current and theintermediate voltage ripple;

FIG. 9 shows a controller that synchronizes a regulating circuit thatprecedes a switched capacitor element;

FIG. 10 shows a three-phase controller that synchronizes a three-phaseswitched capacitor element that precedes a three-phase regulatingcircuit;

FIG. 11 shows a particular implementation of the three-phase controllerin FIG. 10; and

FIGS. 12A-12B show timing diagrams of relevant signals from theembodiment in FIG. 11.

DETAILED DESCRIPTION

The apparatus described herein provides a way to control the switchedcapacitor element 12A and the regulating circuit 16A in a modularmulti-stage power converter architecture.

Before describing several exemplary embodiments of controllers for powerconverters that utilize capacitors to transfer energy, it should beappreciated that in an effort to promote clarity in explaining theconcepts, references are sometimes made herein to specific controllersfor power converters that utilize capacitors to transfer energy. Itshould be understood that such references are merely exemplary andshould not be construed as limiting. After reading the descriptionprovided herein, one of ordinary skill in the art will understand how toapply the concepts described herein to provide specific controllers forpower converters that utilize capacitors to transfer energy.

It should be appreciated that reference is also sometimes made herein toparticular frequencies as well as to particular transformation voltageratios. It should be understood that such references are merelyexemplary and should not be construed as limiting.

Reference may also sometimes be made herein to particular applications.Such references are intended merely as exemplary and should not be takenas limiting the concepts described herein to the particular application.

Thus, although the description provided herein explains the inventiveconcepts in the context of particular circuits or a particularapplication or a particular frequency, those of ordinary skill in theart will appreciate that the concepts equally apply to other circuits orapplications or frequencies.

Embodiments described herein rely at least in part on the recognitionthat by synchronizing the switched capacitor element 12A and theregulating circuit 16A, the intermediate voltage VX ripple effect on theoutput voltage VO and the voltage “glitch” can be minimized.

FIG. 3 illustrates a first generic controller 20 that synchronizes theswitched capacitor element 12A and the regulating circuit 16A within thepower converter 10A shown in FIG. 2. The first generic controller 20receives five input signals and provides three output signals. The inputsignals include the input voltage VIN, the output voltage VO, theintermediate voltage VX, a reference voltage VREF, and a clock voltageVCLK. The output signals include the regulation control voltage VR, thefirst phase voltage VA, and the second phase voltage VB. The clockvoltage VCLK sets the period of the regulation control voltage VR andthe reference voltage VREF sets the desired output voltage VO.

Synchronizing the switched capacitor element 12A with the regulatingcircuit 16A causes the intermediate voltage VX ripple to be in phasewith the switching voltage VLX. In this scenario, feed-forward controlis effective if the frequency of the regulating circuit 16A is greaterthan or equal to the frequency of the switched capacitor element 12A,thereby relieving the severe frequency constraint of separatelycontrolled stages.

Additionally, the glitch capacitor CX, shown in FIG. 2, can be removedaltogether if the dead-time interval DT of the switch capacitor element12A occurs when the regulating circuit 16A is not drawing input current.Synchronizing the switched capacitor element 12A and the regulatingcircuit 16A ensures the proper timing between the dead-time interval DTand the interval during which the regulating circuit 16A is not drawinginput current.

One more benefit of synchronizing the switched capacitor element 12A andthe regulating circuit 16A is the ability to open and close the powerswitches S1-S8 in the switched capacitor element 12A when zero-currentis flowing through the power switches S1-S8. This technique is oftenreferred to as zero-current switching. To achieve zero-currentswitching, the dead-time interval DT must occur when the regulatingcircuit 16A is not drawing input current.

FIG. 4 illustrates a controller 20A that is a preferred embodiment ofthe first generic controller 20. The controller 20A can be separatedinto a first control section and a second control section. The controlcircuitry for the regulating circuit 16A is in the first control sectionand includes first, second, third, and fourth control blocks 30, 31, 32,33. In contrast, the control circuitry for the switched capacitorelement 12A is in the second control section and includes fifth, sixth,and seventh control blocks 34, 35, 36. The “link” between the fourthcontrol block 33 and the fifth control block 34 enables synchronizationof the first and second control sections.

In an effort to promote clarity in explaining the operation of thecontroller 20A, FIG. 5 illustrates some relevant signals generated bythe controller 20A. The relevant signals include the clock voltage VCLK,a saw-tooth voltage VSAW, the regulation control voltage VR, theswitching voltage VLX, a filter inductor current IL, the intermediatevoltage VX, the first phase voltage VA, and the second phase voltage VB.Furthermore, FIG. 6 illustrates a close-up of some of the waveforms inFIG. 5, where the regulation control voltage period TSW is the inverseof the regulation control voltage VR frequency.

Referring back to FIG. 4, the first control section within thecontroller 20A uses a linear voltage-mode control scheme to control theregulating circuit 16A. The controller 20A compares the output voltageVO with the reference voltage VREF, thereby producing a residual voltagethat is conditioned by the second control block 31. A resulting errorvoltage VERR is then fed into the third control block 32 where it iscompared with the saw-tooth voltage VSAW. Lastly, the output of thethird control block 32 is further conditioned by the fourth controlblock 33, resulting in the regulation control voltage VR.

The first control block 30 sets the frequency of the regulation controlvoltage VR by generating the saw-tooth voltage VSAW from the clockvoltage VCLK. Additionally, the first control block 30 providesfeed-forward control of the regulating circuit 16A by adjusting the peakvoltage of the saw-tooth voltage VSAW based upon the intermediatevoltage VX. Alternatively, feed-forward control can be implemented byadjusting the error voltage VERR with respect to the input voltage VINor the intermediate voltage VX in the second control block 31.

The second control section within the controller 20A uses a hystereticcontrol scheme to control the switched capacitor element 12A. Thecontroller 20A causes the first and second phase voltages VA, VB tocycle the switched capacitor element 12A back and forth between thefirst network state and the second network state based upon a hysteresisband.

During operation, the sixth control block 35 continuously compares theintermediate voltage VX with a trigger voltage VXL. When theintermediate voltage VX drops below the trigger voltage VXL, the fifthcontrol block 34 is triggered and then waits for a confirmation signal.Once the fourth control block 33 sends a signal informing the fifthcontrol block 34 that it is acceptable to make a state change, thedead-time interval DT, shown in FIG. 6, is initiated. During thedead-time interval DT, the first and second phase voltages VA, VB areset low. Following the dead-time interval DT, either the first phasevoltage VA is set high and the second phase voltage VB is left low orthe first phase voltage VA is left low and the second phase voltage VBis set high, depending upon the initial state. After the state change,the fifth control block 34 is reset and the sequence repeats.

The controller 20A thus forces the frequency of the switched capacitorelement 12A to be submultiples of the frequency of the regulatingcircuit 16A. This constraint is illustrated in FIG. 5, where thefrequencies of the first phase voltage VA and the second phase voltageVB are much lower than the frequency of the regulation control voltageVR. In some practices, the frequency of the second phase voltage VB isas little as a tenth that of the control voltage VR.

Since the switched capacitor element 12A is loaded down by anon-capacitive regulating circuit 16A, the voltage ripple on theintermediate voltage VX is a piecewise linear approximation of asaw-tooth waveform. As used herein, an intermediate peak-peak voltageripple ΔVX is equal to the maximum intermediate voltage minus theminimum intermediate voltage under steady state conditions. Typically,the intermediate voltage VX comprises a high frequency component fromthe regulating circuit 16A superimposed on the lower frequency saw-toothwaveform from the switched capacitor element 12A.

Unfortunately, while the fifth control block 34 is waiting to changestates, the intermediate voltage VX drops a delta voltage ΔVD below thetrigger voltage VXL, as shown by the intermediate voltage VX curve inFIG. 5. Typically, the delta voltage ΔVD is small, especially if thefrequency of the switched capacitor element 12A is much lower than thefrequency of the regulating circuit 16A. The delta voltage ΔVD at mostcan be equal to one-half of the intermediate peak-peak voltage rippleΔVX and this occurs when the frequency of the switched capacitor element12A is equal to the frequency of the regulating circuit 16A.

FIG. 7 illustrates a DC model of the switched capacitor element 12Acoupled between the voltage source 14 and the regulating circuit 16A.The DC model includes a transformer with a finite output resistance RO.Assuming the switched capacitor element 12A delivers an intermediatecurrent IX, the average of the intermediate voltage VX can be calculatedusing

$\overset{\_}{VX} = {{{VIN}\frac{N2}{N1}} - {{IX} \times {{RO}.}}}$The configuration of the switches and capacitors in the switchedcapacitor element 12A sets a voltage transformation ratio N1:N2.Meanwhile, the output resistance RO of the switched capacitor element12A accounts for the energy loss in charging/discharging the pumpcapacitors.

Based upon the waveforms in FIG. 5, the average of the intermediatevoltage VX can be calculated usingVX=VXL−ΔVD+ΔVX/2.

By equating the previous two equations, the intermediate peak-peakvoltage ripple ΔVX can be expressed as

${\Delta VX} = {{2\left\lbrack {{VIN\frac{N2}{N1}} - {{IX} \times {RO}} - {VXL} + {\Delta\;{VD}}} \right\rbrack}.}$Consequently, the intermediate peak-peak voltage ripple ΔVX is functionof operating parameters such as the intermediate current IX and theinput voltage VIN. Additionally, due to the synchronization constraint,the intermediate peak-peak voltage ripple ΔVX is also a function of thedelta voltage ΔVD.

Unfortunately, large variations in the intermediate peak-peak voltageripple ΔVX can overstress the regulating circuit 16A. To minimizevariations of the intermediate peak-peak voltage ripple ΔVX, the triggervoltage VXL, shown in FIG. 4, can be adjusted on the fly. For example,the seventh control block 36 utilizes the input voltage VIN and theintermediate voltage VX to make a decision on the appropriate value ofthe trigger voltage VXL. Therefore, when the input voltage VIN rises,the trigger voltage VXL rises in step.

One key idea illustrated in FIG. 6 is that the dead-time interval DToccurs during the off state of the high-side power switch SH in FIG. 2.To ensure this outcome, there is an upper bound on the duty cycle of theregulating circuit 16A, where a maximum duty cycle DMAX is determinedusing

${DMAX}{{= \frac{{TSW} - {DT}}{TSW}}.}$As illustrated by the equation above, the dead-time interval DT sets themaximum duty cycle DMAX. It is often desirable to minimize the dead-timeinterval DT, thereby widening the duty cycle range of the regulatingcircuit 16A.

It is not uncommon to have a duty cycle limit, specifically if constantfrequency operation of the regulating circuit 16A is required forelectromagnetic compatibility reasons. In these cases, the maximum dutycycle DMAX constraint is not overly burdensome because the feed-backcontrol loop for the regulating circuit 16A would otherwise have a dutycycle limit.

FIG. 8A illustrates the period of the switched capacitor element 12A andthe intermediate peak-peak voltage ripple ΔVX as a function of theoutput current. As the output current decreases, the slope of thevoltage ripple on the intermediate voltage VX decreases. This reducesthe frequency of the first and second phase voltages VA, VB. Due tosynchronization, the reduction in frequency occurs abruptly and only atspecific output current values. The change in frequency takes placewhenever the intermediate peak-peak voltage ripple ΔVX is equal to amaximum peak-peak voltage ripple ΔVMAX divided by two. Consequently, theintermediate peak-peak voltage ripple ΔVX follows a saw-tooth waveformwith a fixed valley voltage. Furthermore, as the output currentapproaches zero, the intermediate peak-peak voltage ripple ΔVXapproaches one-half of the maximum peak-peak voltage ripple ΔVMAX.

With a few modifications to the controller 20A, it is also possible toget the intermediate peak-peak voltage ripple ΔVX to follow a saw-toothwaveform with a fixed peak voltage as illustrated in FIG. 8B. In thisscenario, as the output current approaches zero, the intermediatepeak-peak voltage ripple ΔVX approaches the maximum peak-peak voltageripple ΔVMAX. The main difference between the first approach in FIG. 8Aand second approach in FIG. 8B is the distribution of frequencies andintermediate peak-peak voltage ripple ΔVX across the output currentrange.

The controller 20A depicted in FIG. 4 and described above is one of manypossible implementations of the first generic controller 20 that cansynchronize the power converter 10A or any power converter that includesa switched capacitor element 12A that precedes a regulating circuit 16A.In the modular multi-stage power converter architecture, the switchedcapacitor element 12A and the regulating circuit 16A can be mixed andmatched in a variety of different ways. For example, FIG. 9 illustratesan alternative power converter 10B, wherein a regulating circuit 16Aprecedes a switched capacitor element 12A.

In FIG. 9, a second generic controller 21 synchronizes the regulatingcircuit 16A and the switched capacitor element 12A. The input and outputsignals of the second generic controller 21 are the same as that of thefirst generic controller 20. In the power converter 10B, the regulatingcircuit 16A may include various types of switch-mode power converters,such as a boost converter, a resonant converter, and a fly-backconverter. Similarly, the switched capacitor element 12A may includevarious types of switched capacitor converters, such as aseries-parallel charge pump, a voltage doubler, and a cascademultiplier. Regardless of the selection of either the regulating circuit16A or the switched capacitor element 12A, if the two stages aresynchronized, the frequency of the switched capacitor element 12A willchange in discrete steps as the output current of the power converter10B is varied.

In addition to alternative modular multi-stage power converterarchitectures, it is also possible to synchronize multi-phaseimplementations. FIG. 10 illustrates a three-phase power converter 10Cand a generic three phase-controller 22 that synchronizes the variousstages. The three-phase power converter 10C includes three regulatingsub-elements: a first regulating circuit 16A, a second regulatingcircuit 16B, a third regulating circuit 16C and three voltagetransformation sub-elements: a first switched capacitor element 12A, asecond switched capacitor element 12B, and a third switched capacitorelement 12C. The first, second, and third switched capacitor elements12A, 12B, 12C provide first, second, and third intermediate voltagesVX1, VX2, VX3, respectively.

First, second, and third regulation control voltages VR1, VR2, VR3control the first, second, and third regulating circuits 16A, 16B, 16C,respectively. Furthermore, first and second phase voltages VA1, VB1control the first switched capacitor element 12A; third and fourth phasevoltages VA2, VB2 control the second switched capacitor element 12B; andfifth and sixth phase voltages VA3, VB3 control the third switchedcapacitor element 12C. Additionally, a regulation control bus BVRincludes the first, second, and third regulation control voltages VR1,VR2, VR3. A first phase bus BVA includes the first, third, and fifthphase voltages VA1, VA2, VA3. Lastly, a second phase bus BVB includesthe second, fourth, and sixth phase voltages VB1, VB2, VB3.

FIG. 11 illustrates a three-phase controller 22A that is a preferredembodiment of the generic three-phase controller 22. The three-phasecontroller 22A can be separated into a first control section and asecond control section. The control circuitry for the first, second, andthird regulating circuits 16A, 16B, 16C is in the first control sectionand includes first, second, third, fourth, fifth, and sixth controlblocks 30, 31, 32A, 32B, 32C, 33. In contrast, the control circuitry forthe first, second, and third switched capacitor elements 12A, 12B, 12Cis in the second control section and includes seventh, eighth, ninth,tenth, and eleventh control blocks 34, 35A, 35B, 35C, 36.

The three-phase controller 22A looks very similar to the controller 20Ain FIG. 4, but with additional input and output signals. In thethree-phase controller 22A, a linear voltage-mode control scheme is usedto control the regulating circuits 16A-16C and a hysteretic controlscheme is used to control the switched capacitor elements 12A-12C.Consequently, the operation of the first and second control sections inthe three-phase controller 22A is similar to that described inconnection with FIG. 4.

In the first control section, the first control block 30 sets thefrequency and phase of the first, second, and third regulation controlvoltages VR1, VR2, VR3. The first control block 30 generates first,second, and third saw-tooth voltages VSAW1, VSAW2, VSAW3 that arecompared to an error voltage VERR by the third, fourth, and fifthcontrol blocks 32A, 32B, 32C, respectively. The resulting three outputsare further conditioned by the sixth control block 33 that produces theregulation control bus BVR.

In the second control section, the first, second, and third intermediatevoltages VX1, VX2, VX3 are compared to a trigger voltage VXL produced bythe eleventh control block 36. The output of the eighth, ninth, tenthcontrol blocks 35A, 35B, 35C are further conditioned by the seventhcontrol block 34 resulting in the first and second phase buses BVA, BVB.The ‘link’ between the sixth control block 33 and the seventh controlblock 34 enables synchronization of the first and second controlsections.

In an effort to promote clarity, FIG. 12A illustrates some relevantsignals generated by the three-phase controller 22A. The first, second,and third regulation control voltages VR1, VR2, VR3 are one hundred andtwenty degrees out of phase with each other. Meanwhile, the phasevoltages VA1, VA2, VA3 are shifted in time with respect to each otherthe same amount as their corresponding regulation control voltages VR1,VR2, VR3 are shifted in time with respect to each other. Furthermore,the second, fourth, and sixth phase voltages VB1, VB2, VB3 are onehundred and eighty degrees out of phase with the first, third, and fifthphase voltages VA1, VA2, VA3, respectively.

For example, if the frequency of the first, second, and third regulatingcircuits 16A, 16B, 16C is one megahertz, then the rising and/or fallingedges of the first, second, and third regulation control voltages VR1,VR2, VR3 are separated by one-third of a microsecond. Consequently, therising and/or falling edges of the first, third, and fifth phasevoltages VA1, VA2, VA3 are separated by one-third of a microsecond andthe rising and/or falling edges of the second, fourth, and sixth phasevoltages VB1, VB2, VB3 are separated by one-third of a microsecond.

With a few modifications to the three-phase controller 22A, it ispossible to further shift the first, third, and fifth phase voltagesVA1, VA2, VA3 by one or more whole periods of the regulating circuits16A-16C as illustrated in FIG. 12B.

For example, if the frequency of each of the regulating circuits 16A-16Cis one megahertz, then the period of each of the regulating circuits16A-16C is one microsecond. Assuming a shift of one period, then therising and/or falling edges of the first, third, and fifth phasevoltages VA1, VA2, VA3 are separated by one and one-third of amicrosecond and the rising and/or falling edges of the second, fourth,and sixth phase voltages VB1, VB2, VB3 are separated by one andone-third of a microsecond. Among other benefits, the more uniformspacing of the first intermediate voltage VX1 ripple, the secondintermediate voltage VX2 ripple, and the third intermediate voltage VX3ripple reduces their effect on the output voltage VO.

As in the single-phase case, the glitch capacitor CX can be removedaltogether if the dead-time interval DT of each of the switchedcapacitor elements 12A, 12B, 12C occurs when their correspondingregulating circuits 16A, 16B, 16C are neither sinking nor sourcingcurrent through an inductive element. For example, in a buck converter,the filter inductor is sinking current from the input only a portion ofthe time, whereas, in a boost converter, the filter inductor is sourcingcurrent to the output only a portion of the time. These power convertershave a discontinuous current interval during which current is eithersunk or sourced. Therefore, the glitch capacitor CX is unnecessary ifthe dead-time interval DT of each of the switched capacitor elements12A, 12B, 12C occurs during the discontinuous input current interval.

Both the controller 20A in FIG. 4 and the three-phase controller 22A inFIG. 11 utilize linear voltage-mode control. However, other controltechniques such as non-linear voltage-mode control, peak current-modecontrol, and average current-mode control are applicable as well.

The control circuitry described herein synchronizes the switchedcapacitor elements 12A with the regulating circuits 16A in the modularmulti-stage power converter architecture. Among other advantages, thecontrol circuitry described herein provides a way to minimize the effectof the intermediate voltage VX ripple on the output voltage VO andminimize the production of a voltage ‘glitch’ during the dead-timeinternal DT of the switched capacitor element 12A.

Various features, aspects, and embodiments of control techniques forpower converters that utilize capacitors to transfer energy have beendescribed herein. The features, aspects, and numerous embodimentsdescribed are susceptible to combination with one another as well as tovariation and modification, as will be understood by those havingordinary skill in the art. The present disclosure should, therefore, beconsidered to encompass such combinations, variations, andmodifications. Additionally, the terms and expression which have beenemployed herein are used as terms to description and not of limitation,and there is no intention, in the use of such terms and expression, ofexcluding any equivalents of the features shown and described (orportions thereof), and it is recognized that various modifications arepossible within the scope of the claims. Other modifications,variations, and alternatives are also possible. Accordingly, the claimsare intended to cover all such equivalents.

Having described the invention, and a preferred embodiment thereof, whatis claimed as new and secured by Letters Patent is:
 1. A power convertercomprising: one or more drivers; a clock to generate a clock signal; amodulator to generate a switching frequency to facilitate zero currentswitching (ZCS) of at least some of a plurality of switches duringoperation of the power converter; a regulating circuit to be arranged ina configuration with a switched capacitor network; and a controllercomprising a first control section and a second control section, thecontroller to implement a dead-time interval, wherein the controller togenerate one or more output signals based, at least in part, on theclock signal to control the at least some of the plurality of switchessubstantially in accordance with the switching frequency, and whereinthe one or more output signals to include at least a first controlsignal generated by the first control section to control a period of theregulating circuit and a second control signal generated by the secondcontrol section to control a period of the switched capacitor network.2. The power converter of claim 1, wherein the controller to synchronizethe period of the regulating circuit with the period of the switchedcapacitor network.
 3. The power converter of claim 1, wherein thecontroller to receive one or more input signals and to generate the oneor more output signals based, at least in part, on the clock signal andthe one or more input signals.
 4. The power converter of claim 1,wherein the clock signal comprises a clock voltage and the one or moreinput signals comprise at least one of the following: a referencevoltage; an output voltage; an intermediate voltage; an input voltage;or any combination thereof.
 5. The power converter of claim 1, whereinin the configuration, the switched capacitor network is to receive aninput voltage and to output an intermediate voltage, and the regulatingcircuit is to receive the intermediate voltage from the switchedcapacitor network and to output an output voltage.
 6. The powerconverter of claim 1, wherein in the configuration, the regulatingcircuit is to receive an input voltage and to output an intermediatevoltage, and the switched capacitor network is to receive theintermediate voltage from the regulating circuit and to output an outputvoltage.
 7. The power converter of claim 1, wherein the controller toimplement the deadtime interval, in whole or in part, via at least oneof the following: a linear voltage-mode control; a non-linearvoltage-mode control; a peak current-mode control; an averagecurrent-mode control; a hysteretic control; or any combination thereof.8. The power converter of claim 1, wherein the controller comprises amulti-phase controller.
 9. The power converter of claim 8, wherein themulti-phase controller comprises a three-phase controller.
 10. The powerconverter of claim 1, wherein the at least some of the plurality ofswitches comprise the switched capacitor network.
 11. The powerconverter of claim 1, wherein the dead-time interval to be implementedduring a discontinuous input current interval.
 12. The power converterof claim 1, wherein the first control signal is generated based, atleast in part, on a comparison of a saw-tooth voltage with a resultingerror voltage.
 13. The power converter of claim 12, wherein thecomparison is implemented via a first comparator.
 14. The powerconverter of claim 13, wherein the second control signal is generatedbased, at least in part, on a comparison of an intermediate voltage witha trigger voltage.
 15. The power converter of claim 14, wherein thecomparison is implemented via a second comparator.
 16. The powerconverter of claim 15, wherein the dead-time interval is implementedbased, at least in part, on a confirmation signal indicating that astate change is acceptable.
 17. A controller to implement a feed-backand/or feed-forward control for a power converter, the controllercomprising: a first control circuitry to generate a first signal tocontrol a period of a switched capacitor network; and a second controlcircuitry to generate a second signal to control a period of aregulating circuit, the second control circuitry to be coupled to thefirst control circuitry, wherein the controller to implement a dead-timeinterval between a first network state and a second network state, andwherein the controller to set a frequency of the switched capacitornetwork to be submultiples of a frequency of the regulating circuitduring operation of the power converter to facilitate zero currentswitching (ZCS) of at least some of a plurality of switches comprisingthe switched capacitor network and/or the regulating circuit.
 18. Thecontroller of claim 17, wherein the controller to set the period of theswitched capacitor network to be an integer multiple of the period ofthe regulating circuit.
 19. The controller of claim 17, wherein thedead-time interval to be implemented based, at least in part, on a clocksignal and one or more input signals indicative of at least one of thefollowing: a reference voltage; an output voltage; an intermediatevoltage; an input voltage; or any combination thereof.